The present invention generally relates to a fouling and corrosion detector for industrial processes, and more particularly, to a field-mounted detector for predicting fouling and corrosion of process elements in an industrial process.
Generally, the term “fouling” refers to a build up of surface agents on a surface. Fouling is a common source of failure in heat exchangers, and can be difficult to detect. Heat exchangers are devices that facilitate, for example, the transfer of heat between a process and a fluid circulating within the exchanger. Heat exchangers are used in a number of industrial systems, including reactors, boilers and the like.
Facilitating this thermal exchange is an exchanger core comprised of one or more tubes through which a fluid is continually circulated. As used herein, the term “fluid” refers to a process material in liquid or gaseous state. The fluid is circulated through the exchanger core. In some embodiments, the fluid may be steam, or high or low temperature process materials, which may have corrosive properties.
Generally, the exchanger core is positioned adjacent to and/or in contact with vessels, conduits, or other components of the industrial process so that heat can be transferred between the process and the circulating fluid within the exchanger. Typically, the fluid within the heat exchanger is fed into the exchanger, circulated through the exchanger, and collected on the other side of the exchanger. In many instances, the collected fluid is recycled and re-circulated. Recycling refers to a process of heating or cooling the collected fluid according to the specific implementation. For example, if the fluid circulated through the exchanger is steam, then condensed steam is collected, reheated until its changes phase back to steam, and then circulated back through the exchanger.
Depending on the material used, the circulating fluid that passes through the exchanger may cause corrosion or may contain solids that can plug or coat the exchanger, thereby reducing the efficiency of the heat exchange process. In general, corrosion and fouling may cause significant problems in an exchanger in an industrial process. For example, if a heat exchanger becomes plugged due to fouling or if it fails due to corrosion (such as because seals become corroded and pressure is lost), process fluid fails to circulate through the exchanger core and the efficiency of the heat exchange may be compromised. Additionally, if the exchanger core is used to deliver heat to a process or to remove heat from a process and the exchanger becomes plugged, the process may not reach the desired temperature. Additionally, the process material that exchanges heat with the fluid in the exchanger core may foul or corrode the core from the outside, rendering the exchanger core inefficient.
When an exchanger core becomes fouled or corroded, typically the system is shut down so that the core can be serviced (unplugged, replaced or otherwise repaired). If an exchanger core fails during operation, not only is the system shut down, but the batch may need to be discarded. It is generally desirable to identify impending fouling and/or corrosion and to service the core before it fails.
In the process industry, unplanned plant downtime can be very expensive due both to loss of production and to the cost of shutdown/start up. Although it varies by industry, scheduled maintenance is often much less expensive than a complete plant shut down. The events that lead to unplanned plant downtime can also result in safety issues, environmental issues, and defective products.
Devices for producing diagnostic information and generating alarms are used in process control industries to avoid such unplanned events when possible. Generally, process variable are monitored, and if predetermined limits are exceeded, an alarm condition is reported. Usually the alarm is indicative of a process variable that is out of normal range. The cause is left to be determined or to be inferred from other information available, either in the control room or at the instrument generating the alarm. Conventionally, detection of plugging or coating required a sophisticated analysis of complex Pressure-Volume relationships to determine if the energy balance or efficiency had degraded from a known baseline condition.